kelly



Nov., 24, 1953 Filed Feb. 5, 1949 F. G, 'KELLY LONG SCALE ELECTRICAL INSTRUMENT .35 61a, 3? sa i 60 INVENTOR ffy @l Nov. 24, 1953 l F. G. KELLY 2,660,707

V LONG SCALE LECTRICAL INSTRUMENT Filed Feb. 5, 1949 2 Sheets-Sheet 2 INVENTOR Eederfc Er- Kalk] @Muna-M ATTORNEY Patented Nov. 24, 1953 UNITED STATE Thomas A. Edison,

Incorporated, West Orange, N. J., a corporation of New Jersey Application February 5, 194.9, Serial No. 74,820

63 Claims. (Cl. 324-440) This invention relates to electrical. instruments and particularly to moving-coil instruments of the long-scale ratio measuring type.

Long-scale ratio measuring instruments are well known in the art but have been complicated and expensive, diflicult to produce with uniform characteristics and difficult to service. By the present invention, such instruments are provided which are relatively simple and economical to manufacture, which are arranged so that critical tolerances can in practice be held to close limits to enable the instruments to be produced with uniform characteristics, and which can be easily assembled and disassembled for servicing and repair. As to this last respect, a particular feature of the invention is that the rotor can be easily installed and removed, to enable replacement of worn pivots, rotor coils, etc., without disturbing the field structure. A further feature of the invention is that it enables long-range measuring instruments to be produced having a small overall diameter.

These and other objects and features of the invention will be apparent from the following description and the appended claims, reference being had to the accompanying drawings, of which:

Figure l is a sectional View of an instrument according to my invention taken on the line I-l of Figure 2;

Figure 2 is a fractional planv View of this instrument as seen from the dial end thereof;

Figure 3 is a right-hand elevational View of the instrument as it appears in Figure 1;

Figure i is a fractional section taken on the line l-i of Figure l;

Figures 5 and 6 are fractional sections taken on the lines 5-5 and 6--6 respectively of Figure 1;

Figure '7 is a fractional elevational view, similar to Figure 3, showing a modified form of instrument according to my invention;

Figure 8 is a Yfractional section on the line 8--8 of Figure 7;

Figure 9 is a fractional section on the line 9-9 of Figure 7; and

1Figure l0 is a :fractional elevational view of the lower one-half portion of the field structure according to a second modication of my invention.

The illustrative embodiment of my invention shown in the accompanying figures comprises a permanent-magnet' field structure including two arcuately-shape'd permanent magnets it and il mounted on acommon axis which is the pivot axis The pole members are made of soft iron or of materials having similar magnetic properties, the term soft iron being herein employed to refer to any such suitable materials. Each magnet pole member has a radially-extending base portion at one end. Preferably, these base portions are aligned in parallel relation with the common axis of the eld structure. Spacers i4 of soft iron are interposed between the base portions of each magnet and the respectively cooperating pole member, and a thicker spacer i5 is interposed between the two pole members'. Passing through the base portions of thelmagnets, pcie members and spacers is a bolt It which clamps the parts in stacked relation and holds them into a unitary structure.

The magnets and their cooperating pole' members have confronting faces separated by air gaps through which flows the useful fiux of the instrument, there being such a gap l1 between the magnet is and pole member it and a gap iii between the magnet li and pole member i3.

" A feature of the present instrument is that these air gapsv can be made uniform and to very close tolerances since they appear between planar confronting faces which can be ground fiat to any desired degree of precision. In the same respect, the magnets and pole members can be heldin true parallel relation by grinding the opposite faces of the spacers it flat and parallel,

The magnets are magnetized to have a varying magnetomotive force along their arcuate length and to provide thus a varying magnetomotive force across the air gaps along the' lengths of the latter. Thus, the iiux density of the gaps is a' minimum at the spacers lli and a maximum at the free ends of the magnets.v The magnetizing of each magnet is carried out after it has been permanently assembled with its-cooperating pole member by filling the slot between the base and free ends of the magnet--which is, for instance, the slot 63 of the magnet iQ-with a soft iron piece tc complete a ring, then inserting a conductive bar through the ring and feeding a current impulse of the order of 20,300 aniperes through the bar. Next, the soft iron piece is removed, and an alternating current is fed through the bar to reduce the magnetization of the magnet by about for stabilizing purposes.

Preferably, the magnets and pole members are rectangular in cross section; however, the magnets are typically made thicker than the pole members since the latter will usually carry flux at higher density. Fora long-scale instrument having scale length of 270 the arcuate length of each magnet and pole member from the medial line of its radially-extending base portion to its free end is typically of the order of 315.

In order to hold the magnets and pole inembers in true coaxial relationship, the radiallyextending base portions thereof are shaped uniformly and formed with flat parallel sides, and a channel bar i3 is fitted thereon along the length of the iield structure. This bar is held in place, for example, by screws 2Q which thread into the intermediate spacer l5.

A rotor 2l for the instrument comprises a shaft 22 having pivots 23 at its ends which engage V- jewel bearings mounted in screws Zl-hereinafter referred to as jewel screws-to pivotally support the shaft at the central axis of the held structure. The upper jewel screw 2d is threaded into an arm 25 having side wings in its base held by screws 26 to like side wings of a pedestal 2l. This pedestal has a block-shaped base 27a clamped to the base portion of the magnet l@ by the bolt I6. Embracing this block is an end portion of the channel bar I9, the base being secured to the channel bar by two screws 2B. At the other end of the instrument there is a block 29 also embraced by the channel bar i3 and clamped against the base portion of the low-or magnet II by the bolt I6, the block 29 being secured to the channel bar by screws 30. Clamped by the bolt I6 against the lower face of the block 29 is a member 3 I having a downwardly offset arm 3m terminating at the central axis of the strument and provided with an aperture 32. This aperture is surrounded by a depending threaded flange 33 for receiving parts hereinafter described. Clamped between the member 3i and the block 29 are two blades 33 which are held in place by the bolt I6 and by a screw 35 that passes through the member 2 I and is threaded into the block 29. The free end portions of the two blades have openings aligned with the central axis of the eld structure. These openings are surrounded by flanges 3S struck from the blades, the liange on the upper blade being extended upwardly and that on the lower blade downwardly. These flanged openings are threaded to receive the lower jewel screw 2d. The free end portions of the blades are biased apart, but are held together as the jewel screw is threaded therethrough, so that upon their release they will exert pressure on the threads of the jewel screw to held the same in its adjusted position.

On the upper end of the shaft 22 there is a flanged collar 37 to which there is staked a cross 38 having three equilength arms at 90 intervals on which are mounted the respective balancing weights 39. This cross has a fourth and longer arm 4I), at a further 90 interval, the major portion of which is offset beyond the upper jewel screw 24 to constitute an indicating pointer.

`other the pole member 'vided on the lower portion of the shaft 22.

This pointer overlies an annular dial 4I that is held onto the upper arm 25 by two screws 32. On this dial there is a graduated arcuate scale d3 with which the pointer d0 registers to indicate the measurements of the instrument.

The rotor 2l includes two coils it and e5, one of which embraces the pole member |12 and the I3. These coils are wound on respective channel frames [i6 and d?, made as of aluminum or copper. These frames 43 and 4l are secured to a bail 48 which in turn is mounted on the central portion of the shaft 22. The frames tt and dl constitute shorted turns on the pole members which, as they cut the flux in the air gaps when the rotor is moved. cause opposing electromagnetic forces to be set up which damp the movement of the rotor, as .is well understood in the art.

Two lead wires of the rotor coils are joined together to form a common lead 33. This common lead and the remaining lead wires and 5l or" the coils (Figure 1) are connected to respective metal disks 43a, 50a and Sia. To these metal disks are connected the inner ends of respective current-conductive hair springs 52, 53 and 55s. These are very light springs arranged to impose a minimum torque on the rotor. The disks 49a- 5Ia are mounted on an insulating sleeve 55 pro- On this sleeve above each hair spring there is an insulating disk 53 which serves as a protective guard for the respective spring. These disks have openings El for the lead wires t9-5I (Figure 5), there being three such openings in the tcp disk, two in the next lower disk and one in the bottom disk. The outer ends of the hair springs are connected to respective pins 58-60 which are carried by an insulating block 3i. This block has a right-angle apertured extension ella secured to the threaded flange 33 by a nut ,l washer generally referred to as 62.

In a ratiometer the torque acting on at least one of the rotor coils must vary with the dellection. Preferably, as in the present instrument, the torque on each of the coils is varied. These torques must oppose each other. This is accomplished in the present instrument by reversing the direction of the lower magnet Il relative to that of the other magnet I0. Notwithstanding the necessity of having one portion of the field structure so reversed, this structure is arranged according to my invention to permit easy installation and removal of the rotor. This is made possible by aligning the slots, which are between the base and free end portions of each pole meinber I2 and I3, and the corresponding slot 33 o the magnet I0 (Figure 4), in parallel relation with the central axis of the eld structure. This requires of course that the pole member I3 be reversed with respect to its cooperating magnet I I, but such reversal is permitted since the magnetomotive force at all points of the pole member is substantially constant. When the slots of both pole members and one of the magnets are so aligned, the rotor can be installed and removed without disturbing the field structure, provided of course that the rotor coils are not displaced axially about the rotor axis by more than the angle subtended at the axis of the field structure by the slots. (Preferably, the coils are mounted coplanar, and the slots are made to subtend an angle of at least 30 to about 45.) To assemble the rotor, for example, the coils are dropped into the slots and the bottom pivot is set into the lower jewel screw 24; next 'fifi rotor is turned to thread the rotor coils onto the respective pole members and the upper jewel screw is mounted into engagement with the top pivot. This ease with which the rotor can. be installed, and likewise removed, is important not only in reducing the cost of manufacture of the instrument but also in that it facilitates servicing of the instrument such, for example, as the re'- placing of worn pivots, the installation of new rotor coils, etc., all of which can be done without disassembling any part of the eld structure or making any change therein that might aiect the calibration of the instrument.

The torque acting on each armature coil, for a given current in the coil, is dependent on the change of ux linkage with the coil caused by an incremental deflection of the coil. The ilux density in the air gap l's' is a minimum at the clockwise end of the gap and increases to a maximum as one proceeds counterclockwise about the pivot axis to the i'ree end of the magnet Il! (Figure e); cn the other hand, the flux density in the air gap it is a minimum at the counterclockwise end thereof and increases to a maximum as one proceeds clockwise along the gap to the free end oi the magnet l l. It is desirable that the tordue-deection characteristic for each coil be substantially linear or, from another viewpoint, that the ux density in the air gaps vary uniformly along the lengths of the gaps since then a more uniform calibration of the instruments can be obtained in production. ln the present instrument, such varying field density is obtained by providing uniform air gaps between each magnet and cooperating pole piece, as heretofore described, and by varying uniformly the magnetoniotive force along the magnet-i. e., providing magnets having uniform magnetizing force. To obtain a uniform inagnetomotive force gradient each magnet should have a uniform composition and be properly shaped. Typically, commercial permanent-magnet materials of the types mentioned have suiiicientiy uniform composition. rThe shaping is preferably such that at each cross section ot the magnet there is a substantially uniform magnetic induction-d. e., flux density. insofar as the gap flux is' concerned, this requires that the thickness dimension oi` each magnet he varied by a square law from' a maximum value at its base end to a minimum value at its free end. However, in view of the linkage flux being mostly at the free end portion of the magnet, a linear tapering of only the free endv portions or the magnets, as at ed and G5 respectively, will cause the magnetic induction to be nearly constant throughout the lengths of the magnets, and will cause a substantially uniformly varying xnagnetomotive force to be produced across the air gaps along the lengths thereof. The tapering of the magnets is however not critical. For instance, when the magnets are sintered, the tapering is formed bythe sintering operation without any further finishing being required.

Prime advantages or the present instrument, whichv are apparent from the foregoing descrip-- tion, lie in the simplicity of its parts, the economy of their manufacture, the ease of assembling them into the nished instrument, and the ease oi removing the rotor for replacing pivots, coils, etc., without disturbing the field structure. It is to be noted particularly that the provision of air gaps between planar parallel surfaces of a magnet and its pole member not only cheapens the construction but also enables the instrument to be produced more uniformly and accurately. The use of effectively long magnets permits cheaper and more easily fabricated magnetl materials to be employed. By arranging the magnets. and pole members.l coaxially the diameter of the instrument is kept small.

While the foregoing features arev particularly beneficial and unusual in a long-scale ratio measuring instrument, it will be apparent from the foregoing description that these features are not limited either to long-scale instruments or to those of the ratio type.

In the modiiied embodiment shown in Figures 7 to 9, the lower element of the permanentmagnet field structure, formerly the magnet ll,

is replaced byl a soft iron arcuatepole member E56 and the lower spacer, formerly the soft iron spacer i4, is replaced by a block-shaped perinanent magnet 67. The pole member t5 has a radially-extending base portion traversed by the bolt i6 and embraced by the charmel bar i9 to hold it permanently in the eld structure in coaxial arrangement with the other elements thereof, the same as was the magnet l l in the former embodiment. The pole member may extend in either direction from its base, it being shown as extending clockwise by way of example. The magnet 67 is magnetized in the direction of the clamping bolt i6 and is preferably made of one of the available aluminum-nickel-cobalt-iron alloys, say that known commercially as Alnico IV having a composition of 12% aluminum, 28% nickel, 5% cobalt and the remainder iron. For efficient design, such a magnet should have about twice the length of the former spacer la, as is shown in the figures. It is undesirable, however, to increase the air gap between the pole member 66 and the adjacent pole member i5, and therefore the pole member 6ft is provided with an offset 68 at the magnet 67, the oiset being between the magnet and a plane through the end face of the adjacent pole member i3 parallel to the axis of the instrument, as shown in the figures, it being understood that the remaining portion of the pole member et is flat and coplanar with the adjacent face of the pole member i3 to provide the uniform air gap it therebetween. rIhev feature of shaping cooperating pole members so that the length of air gap therebetween is less than the length of a blockshaped permanent magnet interposed between the pole members is disclosed and claimed in my co-pending application Serial No. 299,133 filed July 16, 1952.

In this modied embodiment, a magnetic flux is produced in the air gap it by the magnet t?. However, the magnetomotive force at all points on the soft iron pole members i3 and te is substantially constant, and since the air gap i8 is uniform, it follows that the flux density in this air gapy is substantially uni-form. rIhe change in flux linkage withthe coil el on the pole member I3, for' each incremental deflection of the rotor, is therefore constant with the result that a constant torque is exerted on the coil 41 at all positions thereof. rlhis torque is made to oppose the variable torque exerted on' the other coil ist, as by properly selecting the directions of magnetization of the magnet el andof the current in the coil el, so that a trueI ratiometer action is obtained.

In the further embodiment shown in Figure l0, the pole member is, now referred to as i3d, is oliu set downwardly at Se and the pole' member te. now referred to as 6ta, is orset upwardlyV at it,

but each offset is one-half the amount of the' offset 65 in the former embodiment. In this embodiment, the pole members 53a and tta may be identical in shape since one may be mounted in reverse direction to that of the other, as shown, to cause the end portions thereof to be spaced more apart by the respective offsets ti. and 'fil abovementioned. By offsetting the end portion of each of the pole members i3d and 5ta, the shunting eiect of the adjacent portions of the pole members on the magnet is reduced; however, in all essential respects it will be observed that this modified structure is equivalent in its operation to that of the embodiment just described.

The embodiments herein particularly described, which are intended to be illustrative and not limitative of the invention, are subject to changes and modiiications without departure from the scope of the invention, which l endeavor to express according to the following claims.

I claim:

l. An electrical struinent comprising an arou.. ned permanent magnet member less i length, an arcuately-shaped soft iron pole member spaced axi ily from magnet on a common axis therewith to prov e a uniform gap therebetween, a magnetic spacing member between one end of said magnet member and an end of said pole magnet member having opposite poles at its ends and being magnoticed substantially uniformly along the length thereof to provide a inagnetomotive force said gap which v ply the and a movable r vor coil embracing pole member and pivo viid ed at said axis or f 2. An electrical instrument comprising an are ately-shaped permanent magnet magnetized along the length thereof to have opposite poles at its ends, an arcuately-shaped soit iron pole mel ber mounted in coaxial relation with said niagnet and spaced along their common axis from each other, one end portion of said pole member being joined to an end portion oi said magnet, said magnet and pole member having confronting parallel faces uniformly spaced in the direction of said axis from each other along their remain ing portions, said magnet having the free end portion thereof tapered in its thickness dimension to cause the flux density in the magnet to be substantially constant throughout the length of the magnet, and a rotor coil pivoted at the axis of said magnet and. pole member and embracing said pole member.

3. An electrical ratio instrument comprising two arcuatelv-she.ped permanent magnets coaxially arranged, two arcuately-shaped soft iron pole members interposed between said magnets in coaxial arrangement therewith, the end portions of said magnets and pole members being aligned .substantially in parallel with the axis oi the magnets, spacers between said end portions, means clamping said end portions and spacers together in stacked relation, each of said magu nets and its adjacent pole member having confronting parallel faces providing a uniform air gap therebetween, said magnets being magnetized along their lengths to provide a magnetomotive force along said gaps which varies along the lengths thereof, and a rotor pivoted at axis and comprising a pair of coils offset along said axis and embracing said respective pole members.

4. An electrical ratio instrument comprising two arcuately-shaped permanent magnets on a common axis, two arcuatelyshaped softV iron` pole members interposed between said magnets in coaxial arrangement therewith, an end portion of each of said magnets being aligned with a portion of the respectively adjacent pole member and being magnetically joined thereto, and the remaining portions oi each of said magnets and respective pole members being uniformly spaced from each other to provide uniform air gaps therebetween, and a rotor pivoted at said axis and comprising two coils offset along said axis and embracing said pole members respectively, said magnets having a substantially uniform magnetizing force along their lengths to provide a flux in said gaps the density of which varies substantially uniformly along the and the arrangement of said magnets and respec-r tive pole members being such that one of coils moves into an increasing magnetic eld and the other moves into a decreasing magnetic field upon deflection of said rotor.

5. An electrical ratio instrument comprising two arcuately-shaped magnets coaxially arranged, the end portions of said magnets being aligned along the common axis of the magnets and said magnets extending in reverse directions from their said end portions relative to said axis, two arcuately-shaped sort iron pole members interposed between said magnets and having end portions thereof aligned with said end portions of the magnets, said pole members being arranged coaxially with said magnets and both being extended in the same direction from their said end portions whereby the slots between the ends of said pole members and that between the ends of one of said magnets are aligned along said axis, magnetic spacing means joining said end portion or each of said magnets to the said end portion or the respectively adjacent pole member, means holding the magnets and respective pole members in spaced relation to provide uniform air gaps therebetween, said magnets being magnetized along their lengths to provide a magnetomotive force across said gaps which varies along the gaps, and a rotor pivoted at said axis and comprising two coils embracing said pole meinbers respectively, both of which are at the same side of said rotor axis.

6. In an electrical ratio instrument: the combination of two arcuately-shaped magnet members coaxially arranged and having end portions thereof aligned along their common axis, one of said magnet members extending in the reverse direction from the other relative to said axis, two arcuately-shaped soft iron pole members in coaxial arrangement with said magnet roembers, one of which cooperates with one of said magnet members to form one field structure and the other with the other of the magnet members to form a second eld structure, each magnet member and its cooperating pole member being uniformly spaced along said axis to provide a uniform air gap therebetween and being ro agneticalm 1y joined together at one end of said gap, both or" said pole members extending in the same direction relative to said axis from the ends at which they are joined to the respective magnet members whereby the slots which are between the ends of each of the pole members are aligned along said axis with the slot which is between the ends of one of the magnet members, and a rotor pivoted at said axis and comprising two coils, one of said coils embracing one of the members of one of said eld structures and the other 9 of said coils embracing one of the members o1 Number the other of said field structures. 2,440,535 FREDERICK G. KELLY. 2,457,685

References Cited in the le of this patent 5 UNITED STATES PATENTS Number Number Name Date 341629 1,633,912 Vawter 1 June 28, 1927 16,112 1,847,936 Fans Mar. 1, 1932 441,908 1,918,023 Fans July 11, 1933 10 474,887 2,428,209 Fleming Sept. 30, 1947 Name Date Baranowski Apr. 27, 1948 Klepp Dec. 28, 1948 FOREIGN PATENTS Country Date Switzerland Aug. 19, 1905 Great Britain Nov. 15, 1915 Great Britain Jan. 29, 1936 Great Britain Nov. 9, 1937 

